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@article{MS2_1989__65_2_167066, author = {Helmer Aslaksen}, title = {SO(2) invariants of a set of 2 x 2 matrices.}, journal = {Mathematica Scandinavica}, pages = {59--66}, publisher = {mathdoc}, volume = {65}, number = {2}, year = {1989}, zbl = {0679.15029}, url = {http://geodesic.mathdoc.fr/item/MS2_1989__65_2_167066/} }
Helmer Aslaksen. SO(2) invariants of a set of 2 x 2 matrices.. Mathematica Scandinavica, Tome 65 (1989) no. 2, pp. 59-66. http://geodesic.mathdoc.fr/item/MS2_1989__65_2_167066/